1. Field of the Invention
The present invention relates to light-quantity adjusting apparatuses used in optical apparatuses, such as cameras, video cameras, digital cameras or lens apparatuses mounted to them.
2. Description of the Related Art
Electronic cameras, such as video cameras or digital cameras equipped with a solid-state image pickup device, and film cameras using photographic film are provided with a light-quantity adjusting apparatus controlling the size of the aperture in order to adjust the focal depth of the lens and to adjust the light quantity of the field that is to be imaged onto the film or the solid-state image pickup device.
Currently, most light-quantity adjusting apparatuses use a plurality of diaphragm blades as a light-blocking member. Known types include a type in which the aperture diameter is changed continuously with the optical axis in the center, like in an iris, and a type in which the aperture diameter is changed by moving two diaphragm blades substantially parallel in opposite directions.
The former type has the advantage that it is possible to attain any aperture diameter because the aperture diameter is changed continuously. However, a large number of diaphragm blades has to be provided in order to attain an aperture of nearly circular shape, so that there is the disadvantage of higher costs.
On the other hand, the latter type has the advantage of lower costs, because the number of diaphragm blades is small, but the aperture shape changes depending on the aperture area, so that there is the drawback that it is difficult to attain a uniform nearly circular shape.
Furthermore, a technology of combining such a light-quantity adjusting apparatus with an optical filter called an ND filter (light reduction filter) is known, with which the light amount of the imaged field can be controlled over more stages than with diaphragm blades alone.
Furthermore, besides the light-quantity adjusting apparatus, also the shutter device serves as an exposure control mechanism of the camera. Shutter devices can be broadly classified into focal-plane shutters and lens shutters. If the light-quantity adjusting apparatus is provided in a camera equipped with a lens shutter, then the light-quantity adjusting apparatus is arranged adjacent to the lens shutter, so that it is desirable that these apparatuses are provided in a compact manner and fabricated at low cost.
In particular recently, such demands have increased considerably, because the shutter blades have come to be opened and closed by an actuator.
However, in conventional light-quantity adjusting apparatuses proposed in Japanese Patent Laid-Open No. 2000-310803, an actuator 413 for driving the diaphragm blades 404 and an actuator 414 for driving the ND filter 409 are provided separately, as shown in FIG. 20.
Furthermore, if also the shutter blades are driven by an actuator, then a total of three actuators are needed, so that the structural portion related to the light-quantity adjustment becomes large and the camera or lens barrel to which this structural portion is mounted becomes bulky, in addition to higher costs.
It is thus an object of the present invention to provide a light-quantity adjusting apparatus in which a single actuator serves both as an actuator driving a light-blocking member, which are diaphragm blades or diaphragm blades also serving as shutter blades, and as an actuator driving an optical filter, and which can be made more compact and less expensive.
In order to attain this object, a light-quantity adjusting apparatus includes a light-blocking member that changes a quantity of light through an open/close operation within an optical path, an optical filter that can be inserted into and withdrawn from the optical path, independently from the light-blocking member, and a driving mechanism that has a single actuator as a driving source and that drives the light-blocking member and the optical filter. The driving mechanism drives the optical filter by at least one operation selected from operating the actuator further in an opening direction after the actuator has driven the light-blocking member into an open position, and operating the actuator further in a closing direction after the actuator has driven the light-blocking member into a closed position.
These and further objects and features of the invention will become apparent from the following detailed description of preferred embodiments thereof taken in conjunction with the accompanying drawings.